Microphone array technique is one of speech emphasis technique. Concretely, a signal received via a plurality of microphones is processed, and a directivity of the received signal is determined. Then, a signal from a direction along the directivity is emphasized while suppressing another signal.
For example, delay-and-sum array as the simplest method is disclosed in “Acoustic Systems and Digital Processing for Them, J. Ohga et al., Corona Publishing Co. Ltd., April 1995”. In this method, a predetermined delay is additionally inserted into a signal of each microphone. As a result, signals come from a predetermined direction are summed at the same phase and emphasized. On the other hand, signals come from other directions are weakened because their phases are different.
Furthermore, a method called “adaptive array” is also used. In this method, a filter coefficient is arbitrarily updated according to an input signal, and disturbance sounds come from various directions except for a target direction are electively removed. This method has high ability to suppress noise.
Recently, by installing this microphone onto a portable terminal such as a cellular-phone or a PDA, application to clearly catch user's voice becomes popular. In this case, it is an important problem that directivity is formed toward which direction. For example, in case of a cellular-phone, orientation of a user who speaks with the cellular-phone is already known. Accordingly, previous design that directivity is formed toward a direction of the user's mouth is correct.
However, for a mobile speech-to-speech translation device that a plurality of peoples input their voice, directivity should be suitably set to a target person who speaks at the moment.
In order to solve this problem, a terminal has a fixed direction of directivity, and a user moves the terminal in order to keep the directivity set to an appropriate speaker. For example, a reporter moves a microphone between himself and the other party in an interview. However, this method is very troublesome, and there is a possibility that a user cannot watch a screen of the terminal on a direction of the terminal. Furthermore, in case of PDA that orientation (angle) of the terminal changes during use, the user must operate the terminal with conscious of a fixed direction (directivity) of the terminal.
In this way, in case of a terminal having a microphone array that a plurality of speakers inputs their voice, the directivity should be set along a target sound direction which changes depending on various speakers. This operation is very troublesome, and the screen of the terminal cannot be viewed depending on directions of the terminal. Furthermore, in case that orientation of the terminal changes during utterance of different speakers, a directivity direction of the terminal is often shifted from a target sound direction.